Flexible unbonded pipes of the present type are for example described in the standard “Recommended Practice for Flexible Pipe”, ANSI/API 17 B, fourth Edition, July 2008, and the standard “Specification for Unbonded Flexible Pipe”, ANSI/API 17J, Third edition, July 2008. Such pipes usually comprise an inner liner also often called an inner sealing sheath or an inner sheath, which forms a barrier against the outflow of the fluid which is conveyed in the bore of the pipe, and one or more armoring layers. Often the pipe further comprises an outer protection layer which provides mechanical protection of the armor layers. The outer protection layer may be a sealing layer sealing against ingress of sea water. In certain unbonded flexible pipes one or more intermediate sealing layers are arranged between armor layers.
In general flexible pipes are expected to have a lifetime of 20 years in operation.
Examples of unbonded flexible pipes are e.g. disclosed in U.S. Pat. No. 6,978,806; U.S. Pat. No. 7,124,780; U.S. Pat. No. 6,769,454 and U.S. Pat. No. 6,363,974.
The term “unbonded” means in this text that at least two of the layers including the armoring layers and polymer layers are not bonded to each other. In practice the known pipe normally comprises at least two armoring layers located outside the inner sealing sheath and optionally an armor structure located inside the inner sealing sheath normally referred to as a carcass.
These armoring layers comprise or consist of multiple elongated armoring elements that are not bonded to each other directly or indirectly via other layers along the pipe. Thereby the pipe becomes bendable and sufficiently flexible to roll up for transportation.
During transportation, installation and use such unbonded flexible pipes will be subjected to mechanical, thermal and chemical impacts and wear. Usually the unbonded flexible pipe will be qualified to a level beyond what is actually required and often the unbonded flexible pipe will be taken out of use at a time where it is still intact and could have been used for longer time. For a number of years, it has been attempted to incorporate various sensor arrangement into or onto the unbonded flexible pipe to monitor the impacts that the pipe is subjected to and to follow wear and possible damage in order to optimize the use of the pipe and optionally to improve knowledge for use in qualification of future unbonded flexible pipe.
U.S. Pat. No. 7,024,941 describes a method of mounting a sensor arrangement, such as an optical sensor into a reinforcement layer of a flexible pipe. The reinforcement layer is in the form of helically wound metallic armor element(s) and the sensor arrangement is mounted in a groove provided in the metallic armor element where it is fixed with an epoxy material or similar.
WO2008077410A1 describes another method of mounting an optical fiber in an armor element of a flexible pipe, where the armor element comprises a folded metal strip and the sensor placed in a fold of the metal strip for mechanical protection.
WO 2012/059729 describes a flexible pipe with a tensile armor layer of helically wound wires comprising an optical fiber. The optical fiber is arranged in a crush resistant carrier rod in replacement of a wirer of the tensile armor layer.
EP 2065551 describes a flexible pipe comprising a carcass and an extruded polymer layer on the outer side of the carcass wherein a plurality of optical fibers are embedded in the polymer layer for monitoring pressure within the extruded polymer layer. Herein it is also described that a sensor fiber can be incorporated into an armor layer by being arranged in a carrier rod replacing an armor element.
WO2011042023 describes a flexible pipe comprising an internal sheath, at least one armor layer surrounding the internal sheath and a bore defined by the internal sheath where the flexible pipe further comprises a fiber sensor arranged in the bore, such as in a protecting element in the form of a coil or a tube shaped lattice of polymer and/or metal.